This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-101840 filed on Mar. 30, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor package and a method of manufacturing the semiconductor package. In particular, the present invention relates to a technique of improving the reliability of outer lead bonding (OLB) parts of a semiconductor device.
2. Description of the Related Art
As shown in FIGS. 1A and 1B, the wiring layer 30 is formed on a package base 20 and is connected to the semiconductor chip 10 through the contacts 13. These contacts 13 are inner lead bonding (ILB) parts that are sealed with the underfill resin layer 40. The underfill resin layer 40 is extended to the edge of the package. In FIG. 1B, the package is mounted on the board 80 with solder 75.
In FIG. 2A, a package base 20 is provided with ILB parts 13, a wiring layer 30, and package terminals 70 and is covered with an underfill resin layer 40. In FIG. 2B, a semiconductor chip 10 is placed, and electrode terminals of the chip 10 are connected to the wiring layer 30 through the ILB parts 13. In FIG. 2C, the semiconductor chip 10 and underfill resin layer 40 are sealed with a resin mold 60.
As shown in FIGS. 3A and 3B, the package of FIG. 3A differs from the package of FIG. 1A in that it employs no underfill resin and seals contacts (ILB parts 13) between a semiconductor chip 10 and a wiring layer 30 with a resin mold 60.
In FIG. 4A, a package base 20 is provided with ILB parts 13, a wiring layer 30, and package terminals 70. In FIG. 4B, a semiconductor chip 10 is set without underfill resin and electrode terminals of the chip 10 are connected to the wiring layer 30 through the ILB parts 13. In FIG. 4C, the semiconductor chip 10, package base 20, wiring layer 30, and ILB parts 13 are sealed with a resin mold 60.
The underfill resin layer 40 of FIG. 1A must have the following properties:
(1) a high fluidity to collectively seal the ILB parts 13;
(2) a low thermal expansion coefficient xcex1 to improve the reliability of the ILB parts 13; and
(3) a low elasticity modulus E, i.e., softness to improve the reliability of OLB parts, the OLB parts corresponding to contacts between the wiring layer 30 and the package terminals 70.
Generally, a resin having a low thermal expansion coefficient xcex1 has a high elasticity modulus E, and a resin having a high thermal expansion coefficient xcex1 has a low elasticity modulus E. There are resins such as a no conductive film (NCF) having a low thermal expansion coefficient xcex1 and a low elasticity modulus E. This type of resin, however, is expensive.
A semiconductor package employing an underfill resin layer involves the following problems:
(1) low reliability of OLB parts if the underfill resin layer has a low thermal expansion coefficient xcex1 and a high elasticity modulus E to secure the reliability of ILB parts;
(2) low reliability of the ILB parts if the underfill resin layer has a high thermal expansion coefficient xcex1 and a low elasticity modulus E to secure the reliability of the OLB parts; and
(3) increase cost of the package if the underfill resin layer is made from, for example, an NCF to secure the reliability of both the ILB and OLB parts.
The semiconductor package of FIG. 3A is advantageous in that it:
(1) employs no underfill resin layer, reducing process and material costs; and
(2) employs the resin mold 60, which generally has a low thermal expansion coefficient xcex1, thus improving the reliability of the ILB parts 13.
The package of FIG. 3A, however, is disadvantageous in that:
(3) the reliability of the OLB parts is reduced, due to the hardness of the resin mold 60 having a high elasticity modulus E. Namely, the high elasticity modulus of the resin mold 60 on the package terminals 70 causes a concentration of strain at the OLB parts. If the package having no underfill resin layer is large, the reliability of the OLB parts falls critically. In this case, the underfill resin layer must be prepared to improve the reliability of the OLB parts.
When semiconductor packages are diced into individual packages, inferior adhesion between a resin mold and a wiring layer in a package causes a further problem of separating the resin mold from the wiring layer at the edge of the package.
Namely, the semiconductor package having no underfill resin layer involves the following problems:
(1) low reliability of OLB parts; and
(2) peeling on the side faces of the package.
According to an embodiment of the present invention, a semiconductor package includes (a) a package base, (b) package terminals formed on the package base and used to connect the semiconductor package to another device, (c) a wiring layer formed on the package base and electrically connected to the package terminals, (d) a semiconductor chip mounted on the package base and electrically connected to the wiring layer, (e) a low-elasticity resin layer formed between a resin mold and the wiring layer and between the package base and the resin mold, and (f) the resin mold sealing the package base, the wiring layer, the semiconductor chip, and the low-elasticity resin layer. The low-elasticity resin layer has a lower elasticity modulus than the resin mold.
According to another embodiment of the present invention, a semiconductor package manufacturing method includes (a) forming a wiring layer on a package base, (b) electrically connecting a semiconductor chip to the wiring layer, (c) forming a low-elasticity resin layer having a lower elasticity modulus than a resin mold, onto the package base and the wiring layer, and (d) forming the resin mold on the package base, the wiring layer, the semiconductor chip, and the low-elasticity resin layer.